This invention relates to optical sensing arrangements. More specifically, the invention relates to optical sensing arrangements in which optical signals are transmitted along a plurality of discrete optical fibre paths of different lengths which are terminated by respective sensors adapted for sensing temperature, pressure or any other condition to be sensed at appropriate locations and in which optical signals reflected or otherwise caused to be transmitted back along the optical fibres of different lengths in response to the transmission of optical signals along said fibres and in accordance with variations in conditions at the aforesaid locations are detected by optical time domain or frequency domain reflectometer means for determining the conditions at the sensor locations.